Observation on the reduction of the prevalence of malayan filariasis in Chumphon Province of South Thailand.

Further studies on malayan filariasis were made at Bangluke canton of Chumphon province of South Thailand, where mass drug treatment was not applied. It was found after 9 years that there was a marked reduction in filariasis in the area. The filariasis infection rate being decreased from 14.1 to 1.9 per cent, the microfilarial rate from 10.8 to 0.9 per cent, and the elephantiasis rate from 3.3 to 1.0 per cent, and the mean microfilarial density among positive cases being decreased from 27.6 to 6.6 per 20 c.mm blood. Dissection of 1,893 Mansonia mosquitoes revealed the finding of only stage I and stage II larvae of B. malayi in seven M. annulifera and M. indiana. The reduction in the filariasis infection was assumed to be due to the interruption of transmission of filariasis cycle in the mosquitoes resulting from DDT spraying operation of the Malaria Eradication Programme of the Thai Government. There were also some positive cases moving out of the area. The rural development programme of the Thai Government also played another important role in the reduction in the prevalence of malayan filariasis in this area.